This invention relates to an open blade fan for use with a fan clutch such as used in diesel powered trucks, stationary generator sets, etc., and to a method of balancing and to making same.
New emissions standards in Europe and new emission standards to become effective in the year 2002 in the United States require substantial reduction in emissions of hydrocarbons from diesel engines. Current proposals and modifications to diesel engines involve running the diesel engines at higher operating temperatures to reduce emissions. Thus, a greater amount of heat is generated by these diesel engines and this necessitates a greater air flow across the radiator to drop the radiator liquid temperature. Usually, manufacturer specifications specify for a given diesel engine application the volume of air flow needed to drop the cooling liquid""s temperature 1xc2x0 C. across the radiator at given conditions. In some instances, the current open blade fans may be using as much as 60 HP at 2400 rpm to generate about 20,000 cfm to cool engines operating at the current diesel engine temperature conditions. For the newer and hotter temperature engines, the air flow requirement may be as much as 35,000 cfm rather than 2400 cfm for the same truck, diesel generator sets, etc.
A typical approach in the prior art is to use the same fan and to run it at a higher speed than 2400 rpm to obtain the desired 35,000 cfm; but increase of fan speed requires an increase in horsepower and generates more noise. Of course, operating at substantially higher speeds often results in requiring greater strength for the fan to withstand higher forces and stresses because of spinning the fan mass at higher speed. There is a need to balance such fans so that they do not vibrate excessively while spinning.
Open blade fans used with fan clutches are subject to deterioration and a shorter life if they are not properly balanced. Because a truck fan is being driven at high rotational speeds and may be driven by an engine in a truck that may be bouncing over a rough highway, the fan is subject to various forces and vibrations that add stress to the rotating fan blades. Particularly, plastic fan blades being subjected to high ambient heat, as in desert areas and high engine heat outputs beneath a truck hood, can deteriorate and have a shorter life if subjected to high stresses due to vibrations caused by the fan being out of balance. Conversely in very cold, frigid climates and in winter, the plastic of the plastic fan blades tends to become more brittle and it is undesirable to stress these fan blades with high stresses due to fan blade vibration from out-of-balance fan blades.
One conventional manner of balancing open fan blade types of fans having plastic blades is to sever a piece of a fan blade plastic and then spin the fan and observe whether or not there is an improvement in ran balance. If the first saw cut of plastic failed to achieve the desired cut, then a second cut of plastic is made. Obviously, such a trial-and-error method of balancing a fan requires a skilled operator and is very subjective. A shortcoming of cutting plastic from fan blade tips in order to balance the fan blade rotation is that the shortened blade has a greater clearance with the surrounding shroud. From a fan efficiency standpoint, it is undesirable to increase the distance between the fan blade tip and the shroud housing.
Another prior method of balancing plastic fans of this type was to locate the center of balance in a central metal hub plate which is located at the center or hub of the fan and to which the plastic fan blades are attached. Having located the center of balance on the metal hub plate, a new mounting hole can be made at this center of balance and a circular series of bolt-receiving holes can be made about the newly-centered hole to locate the fan rotational axis at the center of the new central mounting hole. Such a secondary operation is time consuming and expensive, and results in fan blade tips that are not equally spaced from the rotational axis thereby increasing the distance between the shortest fan blade tip from the shroud with a concomitant decrease in fan efficiency.
Another problem with plastic, open blade fans of this kind having a central metal plate is the use of electro-plating techniques to coat the central metal hub plated with a corrosion-resistant coating. It has been found that electroplated coats may be uneven with heavy plate areas and lightly plated areas. Thus, the lightly coated areas are subject to corroding particularly in bad corrosive environments to which a truck or generator fan may be exposed. Also, these heavy spots and lighter spots of corrosion-resistance coating tend to throw the fan off balance. Some fan blades are spray painted with uneven coats of paint that also allow corrosion at lightly coated areas. Uneven paint coatings may also add to the fan balancing problem. Thus, there is a need for a new and improved manner of coating the metal fan hub plates that provide an improved, more uniform coating to resist corrosion and that also doesn""t add to the fan balancing problem.
Additionally, it has been found that, in some instances, fan blade deterioration may have been due to exposure of the plastic blades to ultra-violet light from sun rays. For example, if the plastic fan blades are used in a generator set in a very sunny desert location, the plastic of current fan blades may be adversely affected by prolonged exposure to high-intensity UV light. Thus, there is a need to provide a UV plastic fan for use in such environments.
In accordance with the present invention, there is provided, as contrasted with the prior art, a new and improved plastic, open blade fan for use with trucks, diesel engine driven generator sets, etc. In accordance with another important aspect of the invention, an open blade, plastic fan is balanced with a new and improved method that comprises a spinning of the fan blade about its rotational axis and sensing vibrations from the spinning fan; stopping rotation of the fan; specifying locations on the plastic fan body to receive a clip weight; and attaching the clip weight to the plastic body at the specified locations, preferably by clipping of the clip weight to the plastic of the plastic fan body. Preferably, the method includes the providing of clip weights with integral barbs, hooks, or the like, that can be pushed into the plastic with barbs or hooks resisting a throwing off of the weights at high rotational speeds of the fan. In this illustrated and described embodiment of the invention, the fan body is provided with a circular array of integral molded ribs and metal channel-shaped clip weights are pushed over the ribs at the selected locations with integral barbs on the channel-shape clip weights piercing the plastic of the ribs. Herein, the plastic ribs have an outer contour, such as a rounded surface, and the weights have a complimentary shape to allow intimate contact across substantially an entire, inner concave surface of the channel-shaped clip and the outer, convex, rounded surface of the plastic rib. This helps in balancing and in retention of the clip weights on the ribs at high rotational speeds of the fan.
In accordance with another aspect of the invention, the metal hub plate of the plastic fan is provided with an improved corrosion-resistant coating and a more uniform thickness of coating for assisting in the balancing of the fan. This is achieved by using an electrostatic spray coating of the metal plate with a substantially uniform, electrical charge on the metal plate to attract the coating particles to the plate in a uniform manner that results in a more uniform thickness of coating on the metal plate. The preferred coating is an electrostatic paint. This eliminates thinly coated areas that allow corrosion, good adhesion of the paint to the metal, and a balanced uniformly thick coating that assists in the balancing of the fan. The metal plates are electrostatically painted before being molded in situ with the plastic fan body.
In accordance with the preferred embodiment of the invention, the fan body is made of plastic that has improved resistance to deterioration by UV light from sunlight. This is achieved by adding to the plastic a UV addition prior to molding the fan blades and the fan blade body. That is, the preferred UV additive is blended into the bulk plastic by the plastic suppliers. Herein, the preferred UV fan blades are made of nylon that is reinforced by glass particles and rendered UV-resistant by a UV additive to the plastic.